As a method for producing a carrier, a method in which bacteria or enzymes are included in a polymer gel (inclusion method) has been so far known, and it has been industrially utilized.
However, the ordinary method depends on a phenomenon that trace metal elements or inorganic nutrient salts useful for growth of bacteria are diffused and moved from an external culture solution to the inside of a carrier. Accordingly, a diffusion rate of these materials is controlled by the growth of bacteria. Further, since a metabolized substance has resistance to diffusion onto a surface of a carrier, which sometimes hinder the growth of bacteria. Still further, when a gaseous substance is metabolized, floating or destruction of a carrier occurs. Furthermore, in the ordinary method such as the inclusion method, the activity of bacteria is notably decreased owing to toxicity of a polymer used. Therefore, even when a density of bacteria is increased, the activity thereof is not necessarily proportional to the density of bacteria. These are the problems of the ordinary method.
In order to solve these problems, a surface-binding-type carrier was developed in which bacteria and the carrier are physicochemically adhered.
Nevertheless, since this method depends on the physicochemical adhesion between a viscous polymeric substance secreted in the growth of bacteria and the carrier, the growth of bacteria is controlled by the composition of inorganic nutrient salts or trace elements of a liquid entered from an external solution. Moreover, it involves problems that when bacteria present on a surface of a carrier flow within a bioreactor, peeling of bacteria occurs and high-density enrichment culture is naturally restricted.